Generally, smoke detectors detect the presence of smoke particles as an early indication of fire. Smoke detectors are typically used in closed structures such as houses, hotels, motels, dormitory rooms, factories, offices, shops, ships, aircraft, and the like. Smoke detectors may include a chamber that admits a test atmosphere while blocking ambient light. A light receiver within the chamber can receive a level of light from an emitter within the chamber, which light level is indicative of the amount of smoke contained in the test atmosphere.
Several types of fires can generally be detected. A first type is a slow, smoldering fire that produces a “gray” smoke containing generally large particles, which may be in the range of 0.5 to 1.2 microns. A second type is a rapid fire that produces “black” smoke generally having smaller particles, which may be in the range of 0.05 to 0.5 microns. Fires may start as one type and convert to another type depending on factors including fuel, air, confinement, and the like.
Generally, two detector configurations have been developed for detecting smoke particles. One exemplary type of detector is a detector that aligns the emitter and receiver such that light generated by the emitter shines directly into the receiver. Smoke particles in the test atmosphere interrupt a portion of the beam thereby decreasing the amount of light received by the emitter. These detectors can work well for black smoke but are less sensitive to gray smoke. Additionally, such detectors typically are not within a chamber, as they have an emitter and a receiver spaced at a substantial distance, such as one meter or across a room, whereas smoke detector chambers are preferably located within a compact housing. Another exemplary type of detector are indirect or reflected detectors, commonly called scatter detectors, which typically have an emitter and receiver positioned on non-colinear axes, such that light from the emitter does not shine directly onto the receiver. Smoke particles in the test atmosphere reflect or scatter light from the emitter into the receiver.
Smoke detectors typically use solid-state optical receivers such as photodiodes due to their low cost, small size, low power requirements, and ruggedness. One difficulty with solid-state receivers is their sensitivity to temperature. Additional circuitry that increases photoemitter current with increasing temperature partially compensates for temperature effects. Typical detectors also require complicated control electronics to detect the light level including analog amplifiers, filters, comparators, and the like. These components may be expensive if precision is required, may require adjustment when the smoke detector is manufactured, and may exhibit parameter value drift over time.
Further, detection systems, which include several such smoke detectors, typically only detect smoke. Thus, such a detection system generally needs to include additional detectors to detect other particles besides smoke particles. However, the additional detectors typically result in an additional device in the system that has to be mounted on a building structure (e.g., a wall or ceiling) in addition to the smoke detector. Generally, the smoke detector and additional detector are not in communication with each other, such that if both detectors are emitting a noise based upon the detected particle, the emitted noises are emitted independent of one another.